This invention relates to a driving circuit for driving an electrochromic (EC) display device by utilizing a single source of power.
There are two types of the driving circuits for driving EC display devices, one utilizing two sources and the other one source. According to the two source type driving circuit electrode connected to a common segment is maintained at an intermediate potential whereas the electrodes on the display side are applied with a higher potential than the electrode connected to the common segment at the time of interrupting the display, but with a lower potential than the electrode connected to the common segment at the time of display.
According to the single source type electrode connected to the common segment is supplied with a clock signal or the like and the clock signal is varied between a high level and a low level with a suitable timing. To extinguish the display, the clock signal is made to be at the low level when the driving signal is at the high level. To display an information the drive signal is made to be at the low level while the clock signal is at the high level.
Since the two source drive type requires to use two sources, it can be used for relatively large timepieces such as clocks but is not suitable for small timepieces as wrist watches. For this reason, the single source type driving circuit is generally used for wrist watches.
Among various methods of driving may be mentioned a first system of using a memory effect in which when a drive signal is applied and then removed for display and interruption of display, such states are continued by the memory effect, and a second system in which the driving signal is applied at a constant interval, the driving signal being a pulse signal having a definite period which is determined by taking into consideration the memory time of the electrochromic display device. The first system is generally used for the minute and second digits and in which the driving signal is applied only when the decoder output varies, whereas the second system is usually used for digits in which the display does not change for a relatively long time such as hour, day and month digits. When both the first and second systems are used at the same time, a different type display is also possible.
Although various types of driving circuit for EC display devices have been developed as will be described later in more detail, there was a disadvantage of short-circuiting the electrodes of the display device thus not only causing blur of the display but also increase the power consumption which results in the decrease of the life of the operating source.